Search

The burrowing behavior, growth, and size-dependent burrowing rates of two geoduck species--Panopea globosa and Panopea generosa--from the Mexican coast were assessed during early juvenile development (6-7 mo) using 30-L aquariums with a muddy or sandy sediment substrate. Preburial response time, digging rates, and growth were recorded monthly for organisms with an initial shell length of 5 mm (P. globosa) or 10 mm (P. generosa), and continued for 6 or 7 mo. Organisms were fed Isochrysis sp. (clone T-ISO) at libitum on a daily basis during the experimental period. Digging behaviors included the inflation of the geoduck siphon, followed by expulsion of a water jet through the pedal orifice, in conjunction with coordinated muscular contractions of the foot. Both species exhibited a lag in their burial response time that was related linearly to shell length, with rates of 4.5 min/mm (P. globosa) and 3.4 min/mm (P. generosa). Burrowing rates were independent of shell length and were similar in both species (~0.9-1.4 mm/min) for a size range of 7-36 mm, but were slower in 5-mm seed (0.4 mm/min). Shell growth rate increased linearly with time and was faster in P. globosa (162 µm/day) than P. generosa (61 µm/day). These results suggest that short-term temporary enclosures may be useful for restocking natural populations of geoducks with laboratory-produced seed, at a size as small as 7 mm. [ABSTRACT FROM AUTHOR]

Thirty adult organisms of Panopea globosa, an endemic geoduck species from Baja California, Mexico, were collected monthly during a maturation cycle (October through January). Histological and semiquantitative histochemical changes (total lipids and carbohydrates) were assessed in gonad tissue during the maturation process. Biochemical quantification of proteins, lipids, carbohydrates, vitellogenin, and vitellin was performed on hemolymph and gonad tissues of all specimens. The theoretical diameter of oocytes was also estimated from their surface area, measured in histological sections of gonads. Five distinct gonadal stages were identified in both male and female geoducks, with previtellogenic (PVt)/early spermatogenic (ES) gonads being observed in October. Spawning took place in December/January when the temperature reached a plateau of ~18.5°C. Oocyte diameter varied between 25.5 µm (PVt stage) and 74.8 um during the late vitellogenic stage (LVt). The percent of lipids and carbohydrates evaluated histochemically in females closely mirrored the gonadal stages, as well as the diameter. Quantitative changes in proteins, lipids, and carbohydrates in the hemolymph did not show a clear temporal pattern, yet the level of vitellogenin increased from 16.4 (PVt stage)-47.8 µg/mL (LVt stage) and correlated with the oocyte diameter. The weight-specific content of proteins, lipids, and carbohydrates in the gonads was significantly greater during PVt and ES than the other gonadal stages, and remained relatively constant thereafter. Vitellin content mirrored the evolution of each maturation stage and correlated significantly with oocyte diameter. Vitellogenin or vitellin can be used as a reliable quantitative index of gender and degree of gonadic maturity in females. Hemolymph can be obtained readily from the pericardial cavity without affecting the performance of the organism significantly, which further makes vitellogenin a valuable, nonlethal marker for this genus. [ABSTRACT FROM AUTHOR]

Developmental larval stages of the geoduck Panopea globosa (Dall, 1898) are described for the first time. Growth rate, survival, and the length-size relationship were also assessed at 22°C in five independently reared cohorts. Clearance rates (CR), ingestión rates (IR), dry weight, and organic weight of select larval stages were quantified in two additional runs. Clearance rates and IR were evaluated as a function of cell concentration (50, 100, 200 and 300 cells/µL) of the chrysophyte Isochrysis sp. (clone T-ISO) using static systems. Conspicuous larval stages appeared after 20 h (trochophore), 24 h (straight hinge or "D"), 5-6 day (early umboned), 9-10 days (intermediate umboned), 11-12 days (late umboned), and 12-14 days (pediveliger). The larval period for P. globosa lasted between 12 days and 14 days, and the shell length recorded at settlement ranged from 332-356 µm (mean, 343 ± 4.2 µ). The overall average gross growth rate of the five larval cohorts was ~20 µm/day. The relationship between larval shell length (in micrometers) and organic weight (in micrograms) followed a power function with an exponent value of 2.43, whereas the relationship between dry weight and organic weight was linear. Survival rate was approximately 50% in three larval cohorts and 20% in two cohorts. Clearance rates were inversely related to microalgal concentration regardless of larval size, and ranged from 0.3-1.5 µL/h (D larvae) to 15-59 µL/h (pediveliger, 330µm). On the other hand, IR increased with increasing algal concentration, and reached maximum values at 200 cells/µL, except in D-hinge larvae, which exhibited a maximum IR at all concentrations tested. At the highest concentration (300 cells/µL), premetamorphic larvae inhibited their IR. Overall, IR increased from 57-85 cells/h (D-hinge larvae) to 40- or 50-fold when larvae reached the premetamorphic stage. The current study revealed that P. globosa has a short larval period and high survival rate, and withstands a wide range of food concentrations without inhibiting its IR. Therefore, this species appears to be an excellent candidate for hatchery production. [ABSTRACT FROM AUTHOR]

Changes in shell height, tissue dry weight (TDW), mortality, and biochemical composition of Crassostrea gigas were evaluated at two commercial sites in San Quentin Bay (SQB), Mexico, during the first 9 mo post-settlement. Shell growth rates were 1.5× higher at the mouth (0.36 mm d-1) than the head of SQH (0.23 mm d-1). Tissue dry weight was also 7-to 8-fold higher in oysters from the mouth (2.1-2.16 g TDW oyster-1) than the head of SQB (0.23-0.33 g TDW oyster-1) at the end of the 9-mo experiment. Market size (9 cm) was reached after 9 mo at the mouth and at an estimated age of 13 mo at the head of the bay. Highest mortality occurred within the first month post-settlement (50%-60%) and reached approximately 63% to 87% throughout the whole study period. Proteins (48%-64%) and lipids (2%-9%) were the most abundant biochemical components during early spat development. When oysters reached a size between 48 and 55 mm (shell height) in the fall, glycogen (1%-22%) replaced lipids as the main energy depot. The changeover occurred earlier in oysters at the mouth than in oysters from the head of the bay. It is suggested that between-site differences in growth and biochemical composition in oysters are the result of longer immersion/feeding period experienced by oysters at the mouth of SQB. [ABSTRACT FROM AUTHOR]